This invention relates to a rotary compressor.
Rotary compressors include a rotatable impeller wheel mounted on a rotating shaft. The impeller wheel carries several blades, which are mounted on the hub of the wheel for rotation within a housing. By rotating the impeller wheel, gas, usually atmospheric air, is drawn in through an inlet of the housing and discharged through a diffuser into a volute passage which circumscribes the impeller wheel. The impeller wheel may be rotated, in the case of a turbocharger, by a turbine wheel, or may be rotated by direct mechanical drive in the case of a blower or a supercharger. The air is discharged from the volute to provide charge air to the induction manifolds of an internal combustion engine upon which the device is used. Such compressor wheels, however, are stable only across a relatively narrow operating range. Operation of the compressor wheel outside of this range, in what is commonly referred to as the surge or choke regions, results in dangerous instabilities.
Accordingly, it is desirable to extend the operating range of compressor wheels, while at the same time maintaining maximum aerodynamic efficiency. U.S. Pat. No. 4,743,161 discloses one known way to increase the operating range of a compressor wheel. The compressor wheel discussed in this patent provides ports or openings spaced circumferentially around the housing to permit bidirectional flow of gas into the region of the compressor wheel between the upstream and downstream edges of the compressor blades.